The night before you wish to serve your dinner, place a big pot on the stove and add a gallon of water. Add the salt. Turn the heat to high and bring the water to a roiling boil.
While you are waiting for it to come to a boil, remove the medallions from the fridge and place them onto a cooling rack placed on top of a sheet tray that has edges. Season the medallions with salt on both side. Place them back into the fridge, uncovered, and let them air dry overnight.
Place a large bowl, large enough to hold all the haricots vert, into the sink and fill it halfway full with ice. Fill the bowl with water to make an ice bath.
Once the pot of water on the stove has come to a boil, add the trimmed haricots vert. If all goes as planned, the water should barely stop boiling, but if it takes a second or two, don't worry. Cook the beans just until they turn vibrant green and are just tender. Lean on the al dente side for good measure. Remove them from the water immediately and place them directly into the ice bath making sure all the beans are submerged. By doing this you have immediately stopped the cooking process and prevented the beans from becoming too soft.
Once the beans have cooled, drain them then store them in a covered bowl in which you have paper towel in the bottom to absorb excess moisture. Place them into the fridge until you need them.
Now it's showtime. Heat you oven to 400° F. Place all the ingredients on a sheet tray and set them next to the stove. Have two 12-inch sauté pans on the burners with the heat at medium.
Pepper both sides of the beef medallions.
Turn the heat under front sauté pan to high. Add the enough canola oil to coat the bottom. The oil should shimmy and shake but not smoke. Add the medallions, they should sizzle hard when they hit the pan. Once one side has browned, turn them and quickly brown the other side. Remove the medallions to their sheet tray.
Immediately add a tablespoon of butter to the pan and add the mushrooms. This whole process should move very quickly. Stir the mushrooms. Season them with salt and pepper. They should brown at the edges and become crispy.
Remove the pan from the heat. Add the Madeira and carefully put it back onto the flame. The Madeira may ignite, so be prepared for some flame. Let the Madeira reduce and get syrupy, you should have about a tablespoon in the bottom of the pan.
Add the stock or broth. Let it come to a boil, reduce the heat, and let it begin to reduce.
Move the sauce to the back burner and bring the warm empty pan to the front burner.
Slide the medallions into the oven. This is a good time to heat the plates if you want them warm as well.
Add the butter to the hot sauté pan and when the bubbling begins to subside, add the beans. Season them with salt and pepper. Turn them regularly to keep them from blistering, or let them blister and brown -- it is up to you. They are good both ways.
Turn the heat up on the sauce and add 1 teaspoon of the beurre manie. Swirl it into the sauce and let it come to a boil; it should thicken the sauce. If it is too thin, add the other teaspoon.
Remove the plates from the oven along with the medallions. Make sure the plates aren't too hot. Plate up starting with the sauce on the bottom, then the medallions, and then the haricots vert. Serve.